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Low-emittance (low-E) coatings are microscopically thin, virtuallyinvisible, metal or metallic oxide layers deposited on a window orskylight glazing surface primarily to reduce the U-factor by suppressingradiative heat flow. The principal mechanism of heat transfer inmultilayer glazing is thermal radiation from a warm pane of glass to acooler pane. Coating a glass surface with a low-emittance material andfacing that coating into the gap between the glass layers blocks asignificant amount of this radiant heat transfer, thus lowering thetotal heat flow through the window. Low-E coatings are transparent tovisible light. Different types of low-E coatings have been designed toallow for high solar gain, moderate solar gain, or low solar gain.
In heating-dominated climates with a modest amount of cooling orclimates where both heating and cooling are required, low-E coatingswith high-, moderate- or low-solar-gains may result in similar annualenergy costs depending on the house design and operation. While highersolar-gain glazings perform better in winter, lower solar-gain glazingsperform better in summer. In cooling-dominated climates, the priority isto lower solar gains. Look at the energy use comparisons underWindowSelection to see how different glazings perform in particular locations.
Double-Glazed with High-Solar-Gain Low-E Glass | |
This figure illustrates the characteristics of a typicaldouble-glazed window with a high-solar gain low-E glass withargon gas fill. These windows are designed toreduce heat loss but admit solar gain. High-solar-gain low-E glassproducts are best suited for buildings located in heating-dominatedclimates and are the product of choice for passive solar designprojects. High-solar-gain low-E glass is often made withpyrolytic low-E coatings, althoughsputtered high-solar-gain low-E isalso available. |  |
Double-Glazed with Moderate-Solar-Gain Low-E Glass | |
This figure illustrates the characteristics of a typicaldouble-glazed window with a moderate-solar-gain low-E glass withargon gas fill. These windows are often referredto as spectrally selective low-E glass due to their ability to reducesolar heat gain while retaining high visible transmittance. Suchcoatings reduce heat loss and let in a reduced amount of solar gainmaking them suitable for climates with both heating and coolingconcerns. Moderate-solar-gain low-E glass is often made withsputtered low-Ecoatings, althoughpyrolyticmoderate-solar-gain low-E is also available. |  |
Double-Glazed with Low-Solar-Gain Low-E Glass | |
This figure illustrates the characteristics of a typicaldouble-glazed window with a low-solar-gain low-E glass withargon gas fill. As with moderate-solar-gainlow-E glass, these windows are often referred to asspectrally selectivelow-E glass due to their ability to reduce solar heat gain whileretaining high visible transmittance. Compared to most tinted andreflective glazings, this low-E glass provides a higher level of visiblelight transmission for a given amount of solar heat reduction. Variantson low-solar-gain low-E coatings have also been developed which mayappear slightly tinted. This type of low-E product reduces heat loss inwinter and substantially reduces solar heat gain both in winter and insummer. Thus, low-solar-gain low-E glazings are ideal for buildingslocated in cooling-dominated climates. Low-solar-gain low-E glass is typically made withsputtered low-Ecoatings consisting of either two or three layers of silver (also calleddouble-silver or triple-silver low-E). |  |
Glazing Types |Frame Types |Operating Types |Low-E Coatings |Gas Fills |Spacers
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